package com.hulk.sequence.sequence.impl;


import com.hulk.sequence.exception.SeqException;
import com.hulk.sequence.sequence.Sequence;
import com.hulk.sequence.util.SystemClock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

import java.util.concurrent.ThreadLocalRandom;

/**
 * 基于Twitter的Snowflake算法实现分布式高效有序ID生产黑科技(sequence)——升级版Snowflake
 *
 * <br>
 * SnowFlake的结构如下(每部分用-分开):<br>
 * <br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000 <br>
 * <br>
 * 1位标识，由于long基本类型在Java中是带符号的，最高位是符号位，正数是0，负数是1，所以id一般是正数，最高位是0<br>
 * <br>
 * 41位时间截(毫秒级)，注意，41位时间截不是存储当前时间的时间截，而是存储时间截的差值（当前时间截 - 开始时间截)
 * 得到的值），这里的的开始时间截，一般是我们的id生成器开始使用的时间，由我们程序来指定的（如下START_TIME属性）。41位的时间截，可以使用69年，年T = (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69<br>
 * <br>
 * 10位的数据机器位，可以部署在1024个节点，包括5位dataCenterId和5位workerId<br>
 * <br>
 * 12位序列，毫秒内的计数，12位的计数顺序号支持每个节点每毫秒(同一机器，同一时间截)产生4096个ID序号<br>
 * <br>
 * <br>
 * 加起来刚好64位，为一个Long型。<br>
 * SnowFlake的优点是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞(由数据中心ID和机器ID作区分)，并且效率较高，经测试，SnowFlake每秒能够产生26万ID左右。
 * <p>
 * <p>
 * 特性：
 * 1.支持自定义允许时间回拨的范围<p>
 * 2.解决跨毫秒起始值每次为0开始的情况（避免末尾必定为偶数，而不便于取余使用问题）<p>
 * 3.解决高并发场景中获取时间戳性能问题<p>
 * 4.支撑根据IP末尾数据作为workerId
 * 5.时间回拨方案思考：1024个节点中分配10个点作为时间回拨序号（连续10次时间回拨的概率较小）
 *
 * @see： http://git.oschina.net/yu120/sequence
 * @version 3.0
 */
public final class SnowflakeSequence implements Sequence {

	private static final Logger log = LoggerFactory.getLogger(Sequence.class);
	/**
	 * 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
	 */
	private final long twepoch = 1288834974657L;
	/**
	 * 机器标识位数
	 */
	private final long workerIdBits = 5L;
	private final long datacenterIdBits = 5L;
	private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
	private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	/**
	 * 毫秒内自增位
	 */
	private final long sequenceBits = 12L;
	private final long workerIdShift = sequenceBits;
	private final long datacenterIdShift = sequenceBits + workerIdBits;
	/**
	 * 时间戳左移动位
	 */
	private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
	private final long sequenceMask = -1L ^ (-1L << sequenceBits);

	private final long workerId;

	/**
	 * 数据标识 ID 部分
	 */
	private final long datacenterId;
	/**
	 * 并发控制
	 */
	private long sequence = 0L;
	/**
	 * 上次生产 ID 时间戳
	 */
	private long lastTimestamp = -1L;

	public SnowflakeSequence() {
		this.datacenterId = getDatacenterId(maxDatacenterId);
		this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
	}


	/**
	 * 有参构造器
	 *
	 * @param datacenterId 序列号
	 */
	public SnowflakeSequence(long datacenterId) {
		if(datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
		this.datacenterId = datacenterId;
	}

	/**
	 * 有参构造器
	 *
	 * @param workerId     工作机器 ID
	 * @param datacenterId 序列号
	 */
	public SnowflakeSequence(long workerId, long datacenterId) {
		if(workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
		}
		if(datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}

	/**
	 * 获取 maxWorkerId
	 */
	protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
		StringBuilder mpid = new StringBuilder();
		mpid.append(datacenterId);
		String name = ManagementFactory.getRuntimeMXBean().getName();
		if (!isBlank(name)) {
			/*
			 * GET jvmPid
			 */
			mpid.append(name.split("@")[0]);
		}
		/*
		 * MAC + PID 的 hashcode 获取16个低位
		 */
		return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
	}

	/**
	 * 数据标识id部分
	 */
	protected static long getDatacenterId(long maxDatacenterId) {
		long id = 0L;
		try {
			InetAddress ip = InetAddress.getLocalHost();
			NetworkInterface network = NetworkInterface.getByInetAddress(ip);
			if (network == null) {
				id = 1L;
			} else {
				byte[] mac = network.getHardwareAddress();
				if (null != mac) {
					id = ((0x000000FF & (long) mac[mac.length - 2]) | (0x0000FF00 & (((long) mac[mac.length - 1]) << 8))) >> 6;
					id = id % (maxDatacenterId + 1);
				}
			}
		} catch (Exception e) {
			log.error(" getDatacenterId: " + e.getMessage());
		}
		return id;
	}

	/**
	 * 获取下一个 ID
	 *
	 * @return 下一个 ID
	 */
	public synchronized long nextId() {
		long timestamp = timeGen();
		//闰秒
		if (timestamp < lastTimestamp) {
			long offset = lastTimestamp - timestamp;
			if (offset <= 5) {
				try {
					wait(offset << 1);
					timestamp = timeGen();
					if (timestamp < lastTimestamp) {
						throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
					}
				} catch (Exception e) {
					throw new RuntimeException(e);
				}
			} else {
				throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
			}
		}

		if (lastTimestamp == timestamp) {
			// 相同毫秒内，序列号自增
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				// 同一毫秒的序列数已经达到最大
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			// 不同毫秒内，序列号置为 1 - 3 随机数
			sequence = ThreadLocalRandom.current().nextLong(1, 3);
		}

		lastTimestamp = timestamp;

		// 时间戳部分 | 数据中心部分 | 机器标识部分 | 序列号部分
		return ((timestamp - twepoch) << timestampLeftShift)
				| (datacenterId << datacenterIdShift)
				| (workerId << workerIdShift)
				| sequence;
	}

	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	protected long timeGen() {
		return SystemClock.INSTANCE.currentTimeMillis();
	}

	/**
	 * 判断字符串中是否全是空白字符
	 *
	 * @param cs 需要判断的字符串
	 * @return 如果字符串序列是 null 或者全是空白，返回 true
	 */
	private static boolean isBlank(CharSequence cs) {
		if (cs != null) {
			int length = cs.length();
			for (int i = 0; i < length; i++) {
				if (!Character.isWhitespace(cs.charAt(i))) {
					return false;
				}
			}
		}
		return true;
	}

	@Override
	public long nextValue() throws SeqException {
		return this.nextId();
	}

	@Override
	public String nextNo() throws SeqException {
		return String.valueOf(this.nextValue());
	}
}